Pertussis activity in King County remains significant and cases continue to be reported in infants, young children, adolescents, and adults, including cases in schools and healthcare settings.  In May 2005, 31 cases have been reported to-date compared with 13 at this point in May 2004.  Healthcare professionals should be vigilant for the diagnosis of pertussis among persons of any age with a cough illness of 2 weeks duration or longer and among persons with a shorter duration of symptoms who have had contact with a pertussis case.  Healthcare professionals are encouraged to review the following information on recognition and management of pertussis.

Pertussis is a highly communicable bacterial infection of the upper respiratory tract that causes toxin-induced damage to the respiratory epithelium. Pertussis begins with mild upper respiratory symptoms and runny nose followed by cough.  Fever is absent or low-grade.  Adolescents and adults with pertussis may have mild illness, experiencing only a persistent cough.  Young infants with pertussis are at risk for severe and potentially fatal illness, and often require hospitalization. Adults and adolescents with unrecognized pertussis are often the source of infection for infants.  The incubation period is 6-21 days after exposure (usually 7-10 days).

Pertussis is described as having 3 clinical stages; however, the stages may not be distinct. The initial catarrhal stage through the first two weeks of cough illness is the most infectious stage. The paroxysmal stage lasts 2 weeks to 2 months and is characterized by paroxysms of cough, between which the patient may look and feel well.  Cough may be worse at night, and in a minority of cases may be associated with an inspiratory whoop.  Coughing may be (but is not always) accompanied by post-tussive gagging or vomiting.  The convalescent stage lasts 2 weeks to several months, and is characterized by an intermittent cough.

Diagnosing pertussis

The CDC pertussis clinical case definition is: A cough illness lasting at least two weeks with either paroxysms of coughing, inspiratory "whoop", or post-tussive vomiting without other apparent cause (as reported by a health professional).  In an outbreak setting, a case may be defined as a cough illness lasting 2 weeks or longer.  The catarrhal stage may be indistinguishable from a mild upper respiratory tract infection.

Diagnostic laboratory tests include nasopharyngeal swab for isolation of B. pertussis (i.e., culture) and polymerase chain reaction (PCR).  Public Health recommends pertussis culture even when PCR is ordered.  Special pertussis medium can be obtained from your contract laboratory, or by calling Public Health – Seattle & King County Laboratory at (206) 731-8950.  If PCR testing is used, PLEASE NOTE THAT DACRON or RAYON swabs are required for PCR specimens.  Calcium-alginate swabs are known to inhibit PCR testing and should not be used to collect samples submitted for PCR.  

A negative pertussis culture or PCR test does not rule-out pertussis when the clinical picture is suggestive of pertussis. Health care providers should always use droplet precautions (surgical mask) in addition to gown and gloves when collecting clinical specimens for pertussis diagnosis.

Treatment and chemoprophylaxis for pertussis: Who should be treated? 

Antibiotic treatment of persons with pertussis may reduce symptoms when given early in the course of illness during the catarrhal stage (first week of illness).  Treatment within 2 weeks of onset of paroxysms is important to limit transmission of disease to family and other close contacts in the community, but has little impact on the course of illness.  Infants younger than 6 months and others with potentially severe disease may require hospitalization for supportive care and management of coughing paroxysms, apnea, cyanosis, feeding difficulties, and other complications such as pneumonia.

Infected contacts of persons with pertussis can develop a severe cough illness or a milder illness that may not be recognized as pertussis.  Because persons with milder cough illnesses can spread the disease, antibiotic prophylaxis is recommended for all close contacts of pertussis cases, regardless of age and immunization history.  Antibiotic prophylaxis can eliminate the organism from the respiratory tract, both interrupting transmission of disease and preventing or modifying symptomatic illness among infected contacts.  Antibiotic prophylaxis for contacts of persons with pertussis is most effective when initiated within 3 weeks of cough onset of the primary case.

In certain high-risk cases and contacts, initiating treatment or chemoprophylaxis after 3 weeks of paroxysmal cough or exposure should be considered.  High-risk cases and contacts include infants aged <1 year or persons with pertussis or suspected pertussis who may expose persons at high-risk of severe disease (health care workers; labor and delivery, neonatal, pediatric and post-partum staff; pediatricians; midwives, labor coaches, pregnant women, other persons who may expose an infant).

Pertussis Treatment & Chemoprophylaxis Recommendations

• Antibiotic regimens for prophylaxis of pertussis are the same as the treatment regimens.

• Erythromycin remains the standard first line drug for treatment of pertussis and prophylaxis of contacts according to the Centers for Disease Control and Prevention (CDC) and American Academy of Pediatrics (AAP).  AAP recommends erythromycin estolate because of higher serum levels obtained than with equivalent doses of erythromycin ethylsuccinate or stearate.

• The recommended dose of erythromycin for pertussis in children is 40-50 mg/kg/day and in adults is 1-2 g/day orally in four divided doses for 14 days (maximum 2 g/day). 
  
  
• Because relapses have been observed after 7-10 days of treatment with erythromycin, 14 days of treatment have been recommended.  One study has suggested that failure rates for persons with pertussis did not differ significantly after 7 days of erythromycin treatment (2.7%, n=74) compared with 14 days (1.06%, n=94).  Although some authors now recommend a seven day course of erythromycin for pertussis, the CDC and the AAP continue to recommend erythromycin for 14 days for treatment and prophylaxis.
  
  
• Erythromycin resistance has been reported infrequently, but should be suspected in cases that fail to respond to erythromycin treatment when initiated within 2 weeks of onset of illness in appropriate doses in patients for whom compliance is documented.  Please contact Public Health for assistance in obtaining antimicrobial susceptibility testing if you suspect erythromycin resistance.
  
  
• Precaution with treatment and prophylaxis of newborn infants: An association between orally administered erythromycin and infantile hypertrophic pyloric stenosis (IHPS) has been reported in infants younger than 6 weeks of age. The risk of IHPS after treatment with other macrolides is unknown. The American Academy of Pediatrics and the CDC continue to recommend erythromycin for prophylaxis and treatment of pertussis. Physicians who prescribe erythromycin to newborn infants should inform parents of the potential risks of developing IHPS and signs of IHPS (including projectile vomiting and excessive irritability). Whenever possible, determination of persons exposed to pertussis should be made with precision to avoid unnecessary prophylaxis in infants. Cases of pyloric stenosis following use of oral erythromycin should be reported to MedWatch (TEL: 800-FDA-1088; website, www.fda.gov/medwatch) and to Public Health at 206-296-4774).

Newer macrolides – azithromycin and clarithromycin

• A recent study that compared azithromycin, administered as 10 mg/kg (maximum: 500 mg) on day 1 followed by 5 mg/kg (maximum: 250 mg) on days 2—5, with a 7-day treatment of erythromycin estolate found azithromycin as effective as erythromycin and better tolerated for the treatment of pertussis in children (Langley JM et al. Azithromycin is as effective as and better tolerated than erythromycin estolate for the treatment of pertussis. Pediatrics 2004;114;96-101)
  
  
• The 2003 American Academy of Pediatrics “Red Book” Report of the Committee on Infectious Diseases states that clarithromycin (15-20 mg/kg/day orally in two divided doses, maximum 1 g/day), and azithromycin (10-12 mg/kg/day orally in one dose; maximum 500 mg/day) for 5-7 days may be as effective as erythromycin.

Trimethoprim-sulfamethoxazole (TMP-SMX)

• TMP-SMZ is the recommended second-line agent by CDC and AAP for patients who cannot tolerate erythromycin.  The recommended dose of TMP-SMX for children is trimethoprim 8 mg/kg/day, sulfamethoxazole 40 mg/kg/day in two divided doses for 14 days.   The recommended dose for adults is trimethoprim 320 mg/day and sulfamethoxazole 1600 mg/day in two divided doses for 14 days.
  
  
• Hypersensitivity skin rash is the most common adverse reaction to TMP-SMZ.  Because of the risk of kernicterus, TMP-SMZ should not be given to pregnant women at term, nursing mothers, or infants aged <2 months.

Other treatment and management issues

• Hospitalization should be considered for infants <6months of age who develop respiratory distress, feed poorly, or become lethargic.  Persons who have suspected and confirmed cases of pertussis should maintain droplet precautions until 5 days of a recommended course of antibiotic treatment have been completed.  In particular, such persons should not have contact with infants and any unvaccinated children.  All household and other close contacts, particularly young children, should be evaluated for possible antibiotic prophylaxis to limit the spread of disease.  Contacts of pertussis cases who develop a cough illness should be evaluated by a health care professional to rule-out pertussis infection.

If you have questions about diagnosis and treatment of pertussis, contact Public Health’s Communicable Disease Control, Epidemiology and Immunization Section at (206) 296-4774.